1. Manufacturing Processes
Grinding(연삭), EDM(방전)
Associate Professor Su-Jin Kim
School of Mechanical Engineering
Gyeongsang National University 1

2. Contents Abrasive and mechanics Grinding
EDM (Electrical discharge machining)
Water Jet Cutting

3. Grinding (연삭)
In grinding, an abrasive material rubs against the metal part and removes a small amount of material.
Reasons for grinding are: The material is too hard to be machined. Tolerance is less than ± mm.
Grinding is a finishing process used to improve surface finish and the tolerance on flat and cylindrical surfaces.
In grinding, an abrasive material rubs against the metal part and removes a small amount of material.
Reasons for grinding are: The material is too hard to be machined. Tolerance is less than ± mm.
©김태용, GNU

4. Abrasives (연삭입자)
Abrasives are harder than conventional cutting-tool materials.
Aluminium oxide, Al2O3
Silicon carbide, SiC
CBN (Cubic boron nitride)
PCD (Poly crystal diamond)
Grit number (입도지수) indicates the size which is a the function of a sieve(체) size. (10: very rough, 100: fine, 500 very fine)

5. Grinding wheel (연삭 숫돌)
Abrasive grains are held together by a bonding material to achieve a high material removal rate.
Bond types (결합제) : ceramic bond, plastic based bond, rubber, metal bonds

6. Mechanics of Grinding (연삭이론)
Cutting tool is an individual irregular abrasive grain
The average rake angle of the grains is highly negative
Cutting speeds of grinding wheels are very high
Power = Specific energy x MRR (material removal rate) ф
Chip
Workpiece
Grain v α
Material
Specific energy (GPa, J/mm3)
Aluminum
7~27
Cat iron
12-60
Low carbon steel
14-68
Tool steel
18-82
Cutting tool is an individual abrasive grain.
an individual grain has an irregular geometry
the average rake angle of the grains is highly negative
cutting speeds of grinding wheels are very high
Cutting power and energy
Power = Specific energy x MRR (material removal rate)
Specific energy used in producing a grinding chip has 3 components: Chip + Plowing + Sliding

7. Temperature Most of the cutting power transfers into heat.
Temperature rise affects the surface properties and causes residual stress on the workpiece.
Use fluid to prevent excessive temperature rise and to improve the surface finish and dimensional accuracy.
CNC grinding, Dressing, Coolant

8. Grinding Wheel Wear (연삭숫돌마멸)
Attritious wear(소모마멸): caused by interaction of grain and workpiece
Grain fracture(입자파괴): caused by excessive attritious wear, Friability is the ability of an abrasive grain to fracture into smaller pieces.
Bond fracture(결합재파괴): if bond is too strong, dull grains cannot be dislodged
Wear
Grain fracture
Bond fracture
Porosity
Grain
Micro crack
Bond
Friability is the ability of an abrasive grain to fracture into smaller pieces.
Grit number indicates the size which is a the function of a sieve size. (Smaller the sieve size, the larger is the grit number. )

9. Dressing
Once the sharp edges of the grinding wheel are worn out, they need to be dressed.
Grinding dressers are used for making different profile on grinding wheel. The dressing of a wheel in order to return the wheel to its original shape.
vitrified bonded dressing tools
single grit diamond dressing tools
Dressing

10. Surface grinding (평면연삭)
Surface grinding involves grinding flat surfaces.
Grinding wheel
25~50 m/s
Small depth
0.01~0.05 mm
Workpiece
0.2~1 m/s
Surface grinding machine

11. Cylindrical grinding (원통연삭)
Cylindrical grinding, internal grinding and thread grinding are done on cylindrical grinders or centerless grinders
Workpiece
Grinding wheel

12. Centerless & Creep-feed grinding
Centerless grinding
Creep-feed grinding : low feed, large depth
Grinding wheel
Regulating wheel
Work-rest blade
Large depth
1~6 mm
Low speed
0.1~1 m/min

13. Ex) Forces in surface grinding
Assume that you are performing a surface-grinding operation on a low-carbon steel
workpiece using a wheel of diameter D = 25.4 cm that rotates at N = 4000 rpm.
The width of cut is w = 2.54 cm, depth of cut is d = cm, and the feed rate
of the workpiece is v = cm/min. Calculate Fc and Fn.
Solution
Material removal rate is
Power consumed is

14. Ex) Forces in surface grinding
Solution
Since power is defined as
Since thrust force is about 30% higher than the cutting force,

15. Finishing Operations (마무리작업)
Coated abrasives (Sandpaper) is used in finishing flat or curved surfaces of metallic and non-metallic parts. Surface finish depends primarily on grain size.
2. Wire brushing produces a fine surface texture and serves as a light material-removal process.
3. Lapping & polishing: Two surfaces are rubbed together with an abrasive between them to creates a smooth and shiny surface

16. Finishing Operations
4. Honing: Abrasive stone scrubs metal woekpiece to improve a surface texture.
Honing engine block

17. Ultrasonic Machining (초음파가공)
Material is removed from the workpiece surface by the process of microchipping with abrasive particles with vibrations between the tool and the surface of the workpiece.
Workpiece
Power
supply
Transducer
Abras
slurry
Tool
©갈창우, GNU
Ultrasonic Knife

18. ECM (Electrochemical Machining, 전해가공)
High rate of electrolyte movement washes metal ions away from the workpiece.
It is used for machining extremely hard conductive materials with soft tool.
Workpiece
Insulating coating
Tool electrode
Pump for circulating electrolyte DC
power
supply
Tank
Electrolyte
(-)
(+)
©갈창우, GNU

19. Electrochemical Grinding (전해연삭)
Combines the processes of electrochemical machining and conventional grinding.

20. EDM (Electrical-Discharge Machining, 방전가공)
Based on erosion of metals by spark discharges.
EDM system consists of electrodes(전극) connected to a DC and placed in a dielectric fluid(방전액).
Electrode
Spark
Workpiece
EDM

21. EDM (Electrical-Discharge Machining)
50~380 V, 0.1~500 A, 50~500 kHz, 1~100 μm3/Hz
Metal removal rate (mm3/min) = Exp const x Current (A) / Meting temperature (°C): MRR = 4x104 I Tw-1.23
1st RC EDM

22. EDM (Electrical-Discharge Machining)
Used to machine high hardness metals like as die by copper of graphite electrode.
Machine

23. Wire EDM( Wire Electric Discharge Machining)
A brass wire is fed through the workpiece submerged in a tank of dielectric fluid.
It is used to cut plates as thick as 0.3 m and to make punches, tools, and dies from hard metals.
- Wire electrode
+ Workpiece
WireEDM
WireEDM

24. Small Hole EDM
EDM drill rows of holes into the leading and trailing edges of turbine blades used in jet engines.

25. Water-Jet Cutting Water jet acts like a saw and cuts the material.
Advantages: start at any location, no heat, no deflection, environmentally friendly.
Water jet cutting uses a high velocity stream of water to cut through sheet metal. The water typically contains abrasive particles to wear the material and travels in a narrow jet at high speeds, around 2000 ft/sec. As a result, the water jet applies very high pressure (around 60,000 psi) to the material at the cut location and quickly erodes the material. The position of the water jet is typically computer controlled to follow the desired cutting path. Water jet cutting can be used to cut nearly any 2D shape out of sheet metal. The width of the cuts is typically between and 0.06 inches and the edges are of good quality. Because no burrs are formed, secondary finishing is usually not required. Also, by not using heat to melt the material, like laser and plasma cutting, heat distortion is not a concern.
5-axis:

26. Abrasive-Jet Cutting Abrasive water-jet cutting
The water jet contains abrasive particles and increases the material removal rate.
Various thicknesses can be cut in single or multiple layers.
Abrasive-jet cutting
High-velocity jet is aimed at a surface under controlled conditions.
Abrasive waterjet:

27. Reference 제일연마: http://www.grinding.co.kr (숫돌)
진영정기: (연삭기)
우진기공:
국일공작소:
두산인프라코어: (방전가공기)